考研英语阅读模拟试题及答案.doc

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1、Ithaslongbeenknownthattherateofoxidativemetabolism(theprocessthatusesoxygentoconvertfoodintoenergy)inanyanimalhasaprofoundeffectonitslivingpatterns.Thehighmetabolicrateofsmallanimals，forexample，givesthemsustainedpowerandactivityperunitofweight，butatthecostofrequiringconstantconsumptionoff

2、oodandwater.Verylargeanimals，withtheirrelativelylowmetabolicrates，cansurvivewellonasporadicfoodsupply，butcangen-eratelittlemetabolicenergypergramofbodyweight.Ifonlyoxidativemetabolicrateisconsidered，there-fore，onemightassumethatsmaller，moreactive，animalscouldpreyonlargerones，atleastifthey

3、attackedingroups.Perhapstheycouldifitwerenotforanaerobicglycolysis，thegreatequalizer.　　Anaerobicglcolysisisaprocessinwhichenergyisproduced，withoutoxygen，throughthebreakdownofmuscleglycogenintolacticacidandadenosinetri-phosphate(ATP)，theenergyprovider.Theamountofenergythatcanbeproducedanae

4、robicallyisafunctionoftheamountofglycogenpresent-inallvertebratesabout0.5percentoftheirmuscles'wetweight.Thustheanaerobicenergyreservesofaverte-brateareproportionaltothesizeoftheanimal.If，forexample，somepredatorshadattackeda100-tondinosaur，normallytorpid，thedinosaurwouldhavebeenabletogene

5、ratealmostinstantaneously，viaanaerobicglycolysis，theenergyof3，000humansatmaximumoxidativemetabolicenergyproduction.Thisexplainshowmanylargespecieshavemanagedtocompetewiththeirmoreactiveneighbors：thecompensationforalowoxidativemetabolicrateisglycolysis.　　Therearelimitations，however，tothisc

6、ompensa-tion.Theglycogenreservesofanyanimalaregood，atmost，foronlyabouttwominutesatmaximumeffort，afterwhichonlythenormaloxidativemetabolicsourceofenergyremains.Withtheconclusionofaburstofactivity，thelacticacidlevelishighintthebodyfluids，leavingthelargeanimalvulnerabletoattackuntiltheacidis

7、reconverted，viaoxidativemetabolism，bytheliverintoglucose，whichisthensent(inpart)backtothemusclesforglycogenresyn-thesis.Duringthisprocesstheenormousenergydebtthattheanimalhasrunupthroughanaerobicglycolysismustberepaid，adebtthatisproportionallymuchgreaterforthelarger